<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .ye{
            width: 600px;
            height: 600px;
            background-color: yellow;
            position: relative;
        }
        .ba{
            width: 400px;
            height: 400px;
            background-color: aqua;
            position: absolute;
            top: 100px;
            left: 100px;
        }
        .er{
            width: 200px;
            height: 200px;
            background-color: tomato;
            position: absolute;
            left: 100px;
            top: 100px;
                            }
    </style>
</head>
<body>
    <div class="ye">
        <div class="ba">
            <div class="er"></div>
        </div>
    </div>
    
</body>
</html>